We synthesized the specific fluorogenic elastase substrate, methyl-O-succinyl-ala-ala-pro-val amino methyl coumarin and have characterized maximum conditions for assay of human leukocyte lysosomal elastase. Also we have perfected the assay for quantitation of the interaction of plasma fractions containing antitrypsin and lysosomal extracts containing elastase. Utilizing the fluorogenic elastase substrate, we observed that the plasma fractions from ten normal subjects inhibited the elastase activity in lysosomal extracts to a significantly greater degree than did the plasma fractions from ten COPD patients. We will screen an additional 600 subjects and patients which we have accumulated in order to determine the validity of this observation in a large group. We also will correlate the degree of inhibition to pulmonary function abnormality and to proteolysis of elastin. Using conventional biochemical techniques, we will fractionate plasma in order to identify the cause of the decreased inhibition of elastase activity in COPD patients.